Abstract
Herein we report the formation of multi-layered arrays of vertically aligned and close packed semiconductor nanorods in perfect registry at a substrate using electric field assisted assembly. The collective properties of these CdSexS1-x nanorod emitters are harnessed by demonstrating a relatively low amplified spontaneous emission (ASE) threshold and a high net optical gain at medium pump intensity. The importance of order in the system is highlighted where a lower ASE threshold is observed compared to disordered samples.
Highlights
Colloidal nanocrystal lasers offer significant promise for low cost, high gain devices that can be synthesized and processed from solution. 1D rod-shaped nanocrystals are of particular interest as they have shown a lower threshold for lasing in addition to exhibiting directional and polarized emission[1,2]
The CdSexS1-x nanorods capped mainly by alkylphosphonic acid were synthesized via a modified method[20] where x could be tuned from 1 to 0.375 while maintaining a highly monodisperse distribution of rods with average aspect ratio γ= 4 (Fig. 1(a))
We have demonstrated lasing from highly ordered cadmium chalcogenide nanorod assemblies deposited at substrates using electric field assisted assembly
Summary
Colloidal nanocrystal lasers offer significant promise for low cost, high gain devices that can be synthesized and processed from solution. 1D rod-shaped nanocrystals (rods, wires, belts) are of particular interest as they have shown a lower threshold for lasing in addition to exhibiting directional and polarized emission[1,2]. Harnessing the collective emission from colloidal semiconductor nanorods through organized assembly has enormous potential for generation lasers with particular interest for their application in integratable nanophotonics as components for all-optical integrated circuits[6,7]. We have achieved strong PL emission in the cadmium chalcogenides system without a core-shell structure by combining the metal cation with both chalcogen anions in an alloy[20] This alloyed nanostructure allows precise tuning of the bandgap as a function of anion ratios allowing for optimization as needed for light emitting applications[21,22]. Lasing from a square cavity (10 μm × 10 μm- patterned by focused ion beam milling) in the assembled film is demonstrated Their ease of assembly from solution, controllable deposition procedures and subsequent compatibility for further processing makes this route an attractive approach for integratable nanophotonics. CdSe0.625S0.375 nanorods with an aspect ratio of 4; (b) The setup for electric field assembly; (c) Cross-section SEM image of vertically aligned multilayer nanorods on a Si substrate. (d) XRD patterns the aligned film (red line) and disordered nanorods (black line); (e) PL characterization of assembled (solid line) and disordered (dash line) films in three compositions: CdSe (blue line), CdSe0.625S0.375 (Se-rich sample, red line), and CdSe0.375S0.625 (S-rich sample, black line)
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